Between the sheets: Sodium-ion batteries are an attractive, low-cost alternative to lithium-ion batteries. Nitrogen-doped porous carbon sheets are prepared by chemical activation of polypyrrole-functionalized graphene sheets. When using the sheets as anode material in sodium-ion batteries, their unique compositional and structural features result in high reversible capacity, good cycling stability, and high rate capability.

Pressing concerns about limited reserve and distribution of lithium resources have led to an increasing interest in replacing lithium-ion batteries (LIBs) from a viewpoint of sustainability. [1][2][3][4][5][6] In response, sodium-ion batteries (NIBs) are an attractive alternative because sodium resources are practically inexhaustible and ubiquitous, for example, the cost of Na 2 CO 3 is only 3% of the cost of Li 2 CO 3 . [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] However, as only a very limited number of materials are reported to be viable up to now, [ 23,24 ] the performance of the NIBs is still terribly plagued by low specifi c capacity, poor rate capability, and short cycle life. On the other hand, the commonly used electrode materials in LIBs and NIBs are rely heavily on depletable metal-based inorganic compounds prepared from limited mineral resources, thus giving rise to the problem of cost and environmental concerns. Therefore, there is an urgent need to prepare future electrode materials, shifting from inorganic to organic materials that are more abundant, from renewable resources with minimum energy consumption. They are also required to have high power density and long cycling stability.Organic materials, and in particular organic carbonyl compounds, are considered to be promising electrode materials due to their numerous advantages, including lightweight, redox stability, multi-electron reactions, and availability from easily accessible natural sources. [25][26][27][28][29][30][31][32][33][34][35][36][37] Furthermore, organic synthesis techniques and quantum chemical considerations enable the performance of batteries to be tuned on the molecular level, that is, to tailor secondary batteries. [ 25 ] Due to the less rigid structure compared to inorganic counterparts, organic compounds are structurally more fl exible and thus could facilitate the higher mobility of large-sized sodium ions, which is vital to the operation of NIBs. [ 38 ] Furthermore, no strongly oxidizing substance would be generated during the charge/discharge process of organic materials, which could at least alleviate the daunting safety problem of the transition metal oxide (TMOs) cathode. [ 29 ] In this context, very recently, organic carbonyl compounds, such as sodium terephthalate and its derivatives, have been developed as promising organic anodes for NIBs. [39][40][41] However, no corresponding organic compounds or aromatic carbonyl derivatives containing dianhydride as cathode materials for NIBs have been successfully developed until now because the direct implementation of organic molecules in battery systems is diffi cult due to the serious dissolution in electrolyte. [ 29,35,36 ] In response, one very promising strategy is to construct dianhydride-based polymer materials to make a stable and fl exible framework, which could restrain the unwanted dissolution in the electrolyte and achieve fast kinetic properties. [29][30][31][32] Based on the structural characteristics of dianhydride, it is a promising altern...

COMMUNICATION Figure 5. a) Cycling performance of binder-free porous CNAs, CuO nanorods scraped off of Cu foil, and CuO nanosheets. b) Rate capability of different CuO electrodes at various current densities from 0.02 to 1 A g −1 . c) Cycling performance of binder-free CNA electrode at a high current density of 200 mA g −1 . d) Schematic diagram showing the strategy for binder-free CNA electrode.www.advmat.de www.MaterialsViews.com wileyonlinelibrary.com

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Ultralong cycle life, high energy, and power density rechargeable lithium‐ion batteries are crucial to the ever‐increasing large‐scale electric energy storage for renewable energy and sustainable road transport. However, the commercial graphite anode cannot perform this challenging task due to its low theoretical capacity and poor rate‐capability performance. Metal oxides hold much higher capacity but still are plagued by low rate capability and serious capacity degradation. Here, a novel strategy is developed to prepare binder‐free and mechanically robust CoO/graphene electrodes, wherein homogenous and full coating of β‐Co(OH)2 nanosheets on graphene, through a novel electrostatic induced spread growth method, plays a key role. The combined advantages of large 2D surface and moderate inflexibility of the as‐obtained β‐Co(OH)2/graphene hybrid enables its easy coating on Cu foil by a simple layer‐by‐layer stacking process. Devices made with these electrodes exhibit high rate capability over a temperature range from 0 to 55 °C and, most importantly, maintain excellent cycle stability up to 5000 cycles even at a high current density.

Three-dimensional (3D) hierarchical Fe 3 O 4 /graphene nanosheet (GNS) composites have been synthesized using a simple in situ hydrothermal method. Characterization shows that the Fe 3 O 4 nanoflowers are highly encapsulated in a GNS matrix. The Fe 3 O 4 /GNSs-1 nanocomposite (60 wt % of Fe 3 O 4 in the composites) exhibits a stable capacity of ∼605 mAh g À1 with no noticeable fading for up to 50 cycles in the voltage range of 0.001À3.0 V, and the superior performance of Fe 3 O 4 /GNSs-1 is clearly established by comparison of the results with those from Fe 3 O 4 /GNSs-2 (23 wt % of Fe 3 O 4 in the composites) and bare Fe 3 O 4 . In addition, another possible application of the drug delivery with the composites shows that the loading of rhodamine B (RB) on Fe 3 O 4 /GNSs increased linearly with the increase in the initial RB concentration, and the loading capacity of Fe 3 O 4 / GNSs-1 was as high as 3.18 mg mg À1 . The excellent electrochemical performance of the composites and highly efficient loading of RB could be attributed to the enhanced electronic conductivity and the large surface areas of the Fe 3 O 4 /GNSs in which the hierarchical structure of Fe 3 O 4 nanoflowers are highly encapsulated in the GNS matrix.

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Supercapacitors, as one of alternative energy devices, have been characterized by the rapid rate of charging and discharging, and high power density. But they are now challenged to achieve their potential energy density that is related to specific capacitance. Thus it is extremely important to make such materials with high specific capacitances. In this report, we have gained homogenous Ni(OH)2 on graphene by efficiently using of a facile and effective electrostatic induced stretch growth method. The electrostatic interaction triggers advantageous change in morphology and the ordered stacking of Ni(OH)2 nanosheets on graphene also enhances the crystallization of Ni(OH)2. When the as-prepared Ni(OH)2/graphene composite is applied to supercapacitors, they show superior electrochemical properties including high specific capacitance (1503 F g−1 at 2 mV s−1) and excellent cycling stability up to 6000 cycles even at a high scan rate of 50 mV s−1.